Generally, fuel amount of a gasoline engine is determined based on a theoretical air-fuel ratio. As fuel amount approaches to the theoretical air-fuel ratio, fuel can be completely combusted in a cylinder and purifying efficiency of a catalyst for purifying exhaust gas is improved.
In order to control the fuel amount to be the theoretical air-fuel ratio, it is important to predict an exact air amount supplied to the cylinder.
Further, recently, a LIVC (late intake valve closing) control is used in order to reduce pumping loss of an engine. The LIVC control means that a closing timing of an intake valve is retarded after BDC (bottom dead center).
However, according to the conventional art, since it does not consider that air flowing into the cylinder at an intake stroke flows backward into an intake manifold at a compression stroke, the exact air amount supplied to the cylinder cannot be calculated and thus an exact fuel amount based on the theoretical air-fuel ratio cannot be calculated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.